Method of extracting and reutilizing surfactants from emulsions with sulfonated alkyl benzenes and alcohols

ABSTRACT

Disclosed is a method for extracting surfactants from produced emulsions of oil, water and surfactant and concentrating the surfactants into a relatively small volume, surfactant-rich, middle phase that can be reutilized in surfactant flooding. A first extraction is performed with an aqueous solution of a first extracting compound, which yields three phases after separation, a substantially water-free and surfactant-free crude oil phase, a first surfactant-rich middle phase and an oil-free aqueous phase. The first extracting compounds employed are the alkali metal salts and ammonium salts of cumene sulfonate, propyl benzene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate. 
     A second extraction is then performed by mixing a second extracting compound with the first middle phase, which yields three phases after separation, a water-free and surfactant-free oil phase, a second surfactant-rich middle phase and an oil-free aqueous phase. The second extracting compound is a alkanol having two to four carbon atoms.

FIELD OF THE INVENTION

This invention is related to copending U.S. patent application Ser. No. 462,579, filed Jan. 31, 1983 and copending U.S. patent application Ser. No. 559,076, filed Dec. 7, 1983. More particularly, the invention relates to the extraction and reutilization of surfactants from oil, water and chemical emulsions that are produced as a result of enhanced oil recovery operations.

BACKGROUND OF THE INVENTION

Surfactant flooding has become one of the more promising enhanced oil recovery techniques for recovering oil after water flooding. Generally, the method of surfactant flooding employs the injection of a surfactant in an aqueous solution or in an emulsion to sweep through the formation and recover oil. It is believed that surfactants are effective because of their ability to reduce the interfacial tension between crude oil and water. This reduction of interfacial tension permits the creation of various oil, water and surfactant emulsions in the formation. Thus, the produced liquids of surfactant flooding are generally very stable oil, water and surfactant emulsions.

Because of the relative amounts of oil and water produced in chemical flooding, the produced emulsions will usually be oil-in-water emulsions. Upon settling, such emulsions may change to the water-in-oil emulsions which are usually encountered in primary petroleum production. Conventional surfactant extraction and emulsion breaking techniques which work on water-in-oil emulsions may be ineffective with oil-in-water emulsions.

Second, the creation of these generally highly stable emulsions results in decreased surfactant reutilization efficiency. Considerable quantities of surfactants are entrained in the produced emulsions which prevents the effective reutilization of the produced surfactant in the continuing surfactant flooding process. Because surfactants are expensive additives for chemical floods, commercial economics require that surfactant costs be minimized by reutilizing a substantial quantity of surfactant that is injected into the formation. In addition, the methods which are available to separate the produced emulsions fail to extract and concentrate the produced surfactant sufficiently enough for reutilization of the surfactant.

One method of breaking an oil-in-water emulsion is described in U.S. Pat. No. 4,029,570 where an additional formation brine is added to the produced emulsion to produce an oil phase and a water phase. However, such brine addition treatments will in many cases not work on produced fluids. One reason is the tendency of formation rock to selectively adsorb high equivalent weight sulfonates, leaving lower equivalent weight sulfonates behind, rendering the surfactant highly hydrophilic. Such processes will not sufficiently extract and concentrate the surfactant to allow reutilization. The surfactant is often left highly diluted in a relatively large volume of oil-in-water emulsion unsuitable for reutilization.

U.S. Pat. No. 3,637,521 discloses an emulsion breaking process comprising the steps of (1) adding an acid to lower the pH of the emulsion to approximately 5.0 and (2) adding an alkylamine containing 1 to 5 nitrogen atoms and from 2 to 12 carbon atoms. U.S. Pat. No. 3,687,845 describes a process wherein oil-in-water emulsions are treated by the addition of a high molecular weight, watersoluble polymer such as the polyvinyl aromatics of benzene such as polystyrene, polyvinyl toluene and several acrylamide compounds.

Another method which has been tried to break oil-in-water emulsions is the use of additional surface active agents. U.S. Pat. No. 4,261,812 discloses a method which employs an additional surface active agent having an average equivalent weight higher than the equivalent weight of the surface active agents in the produced emulsion, preferably an equivalent weight of about 400 to 600. U.S. Pat. No. 4,073,344 mentions the use of dimethylbenzene ammonium chloride, trimethyl ammonium chloride and alkyl benzene sulfonates for the same purpose. The use of additional solubilizers to break oil-in-water emulsions was promoted by U.S. Pat. No. 4,277,352 which suggests adding materials commonly used as solubilizers in surfactant flooding to the produced emulsion.

Although several of the above discussed methods may provide a way to free crude oil from produced emulsions, none of the references provide a process in which the surfactant can be economically recovered and concentrated for reuse.

SUMMARY OF THE INVENTION

The present invention provides for extracting surfactants from produced emulsions of oil, water and surfactant and concentrating the surfactants into a relatively small volume, emulsion phase that can be reutilized in surfactant flooding. The phases left behind in the extractions are substantially water-free and surfactant-free crude oil phases and crude oil-free aqueous phases. Substantial additional quantities of salable oil are freed by this invention from produced emulsions.

The surfactant extraction and concentration method of the present invention is performed by a two step extraction process. The first extraction employs a first extracting compound selected from the group of alkali metal salts and ammonium salts of cumene sulfonate, propyl benzene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate to form three phases, including a crude oil phase, a first middle phase and an aqueous phase. The second extraction step mixes an alkanol having two to four carbon atoms with the first middle phase to form three additional phases, including a surfactant-rich second middle phase.

Optionally, the first and second extracting compounds may be added to the emulsion in a common solution for a one-step extraction process.

DETAILED DESCRIPTION

The extraction of surfactants from produced emulsions by the addition of various hydrotropes solves a difficult problem and permits the reutilization of the relatively expensive surfactants employed in chemical oil flooding operations. A significant advantage is provided by the recovery of additional amounts of crude oil substantially free of entrained surfactant and water impurities.

The present invention is related to a similar surfactant extraction process disclosed in copending U.S. patent application Ser. No. 462,579, filed Jan. 31, 1983, the disclosure of which is fully incorporated herein by reference. This invention comprises extracting surfactants from produced water-in-oil or oil-in-water emulsions by the addition of two extracting compounds. Oil-in-water emulsions are handled by first inverting them to water-in-oil emulsions by procedures well known in the art. One such procedure involves the addition of calcium ions and/or petroleum sulfonate blend.

In the preferred embodiment, the first extracting compound is added to the produced emulsion in an aqueous solution of about 0.3% to about 6%. The first extracting compound is selected from the group consisting of the alkali metal salts and ammonium salts of cumene sulfonate, propyl benzene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate, and dicyclopentadiene sulfonate. Ammonium salts offer very similar performance to alkali metal salts in enhanced oil recovery applications. The sodium salts of the above compounds are preferred.

During an appropriate settling time of about thirty to about sixty minutes, which may be considerably shorter or longer depending on conditions, most of the surfactant will partition into a first relatively low volume, surfactant-rich emulsion middle phase. The crude oil phase which is partitioned is almost completely free of any surfactant or brine contamination. An oil-free aqueous phase is also partitioned which contains excess extracting compounds.

About 0.5% to about 3% by volume of second extracting compound is added and mixed with the first surfactant-rich middle phase. If desired, the second extracting compound can also be incorporated in an aqueous solution for addition. The second extracting compound is a alkanol having two to four carbon atoms with isopropanol being the most preferred alkanol. Other possible second extracting compounds are: ethanol, n-propanol, butanol, isobutanol and mixtures thereof. Because of the relative costs of the compounds, a mixture of isopropanol and ethanol is also preferred.

The mixture of alkanol and first middle phase will separate into three phases during an appropriate time, which may be about thirty to about sixty minutes or longer depending on conditions. As in the first extraction step, the three phases will be an upper surfactant-free and water-free crude oil phase, a second middle phase which is a surfactant-rich microemulsion, and a lower aqueous phase containing significant quantities of first and second extracting compounds. The lower aqueous phase can be recycled for additional extractions.

The second middle phase left after the second extraction is substantially smaller in volume than the first middle phase. The decrease in volume is primarily due to the release of significant amounts of crude oil and brine from the first middle phase, resulting in a further concentration of surfactant in a relatively small volume middle phase.

In one of several alternate embodiments, the first and second extracting compounds are added to the emulsion in a common aqueous solution for a one step extraction process. In another embodiment, the middle phase and the lower aqueous phase from the first extraction step are mixed together with the second extraction compound to yield the final three phases including the surfactant-rich second middle phase. In a fourth embodiment, the middle phase and the lower aqueous phase from the first extraction step are mixed together and allowed to separate into two phases, an upper phase and a lower aqueous phase. The second extraction step is then performed on the upper phase yielding the final three phases including the relatively lower volume, surfactant-rich, second middle phase.

It should be noted that liquids may not settle into separate distinct phases all the time. At times, there may be a small boundary area between two phases which does not distinctly belong to either phase. Sometimes, a complete separation into several phases may take days. Thus, whenever the words "separate" and "separation" are used herein, they refer to a separation that is preponderantly complete.

At times, the addition of water or brine as well as clean crude oil to the emulsion before addition of the extracting compound will aid in extraction efficiency. As in other steps of the extraction and reutilization process, fresh water and brine may be used interchangeably. Although different brines may require different extracting compound concentrations, the process yields excellent performance in both high and low salinities. Thus, fresh water may be used in the process where brine is mentioned, and brine may be employed where water is noted.

The surface active agents extracted may be the commonly used anionic surfactants such as petroleum sulfonates or nonionic surfactants. More specifically, the inventive method extracts surfactants such as alkylaryl sulfonates, alkoxylated alkyl phenol sulfonates, alkoxylated alkylphenol sulfates, alkoxylated sulfonated or sulphated alcohols.

Other materials which may be present in the produced emulsions are various thickening agents such as biopolymers and synthetic polymers, e.g., polysaccharides and polyacrylamides. Salts which occur naturally in the formation or were added to the flooding water may be present. Additionally, the invention process is also effective in extracting surfactants from emulsions which contain various solubilizers, which are usually added to enhance surfactant solubility. These solubilizers include the water-soluble alcohols or polyhydric alcohols, ether alcohols, alkoxylated phenols and alkoxylated alkyl phenols, alkoxylated alcohols, polyalkoxylated mercaptans, as well as the sulfated or sulfonated derivatives of the alkoxylated phenols or the alkoxylated alcohols.

Produced emulsions will normally be in the form of oil-in-water emulsions and water-in-oil emulsions. Many times, an oil-in-water emulsion will separate over time with the aid of gravity to a water-in-oil emulsion and an aqueous phase. Oil soluble sulfonate surfactants usually speed up this process.

Certain pretreatment steps may be optionally employed to improve the extraction and concentration of the surfactants in the two middle phases. Separation by gravity of the produced emulsion into predominantly oily and aqueous phases will reduce the volume of produced oily emulsion to be treated by the extraction method. Likewise, the employment of a heater treater or similar apparatus to process the produced emulsion prior to the extraction method will also substantially reduce the volume of the emulsion to be treated, as well as improve the efficiency of the extraction method.

Third, the addition of oil soluble, high equivalent weight surfactants to the produced emulsion may also significantly aid gravity separation in reducing oily emulsion volume. Sulfonate surfactants which tend to be oil soluble and have an average equivalent weight within the range of about 400 to about 600 are especially preferred for pretreatment of the produced emulsions. One example is the compound sold under the tradename TRS-18 by Witco Chemical Company having an equivalent weight of about 500. This oil soluble sulfonate may be added in concentrations ranging from about 0.5% to about 4.0%. However, the later addition of a water soluble sulfonate surfactant may be required for efficient extraction by the present invention when such oil soluble sulfonates are added during the pretreatment step.

The presence of certain polymers in the produced emulsion may also require a pretreatment washing step. Some biopolymers such as polysaccharides may cause the creation of a fourth phase and inhibit each extraction of surfactants into the middle phase with the method of the instant invention. But it has been discovered that the effect of these polymers on the extraction method can be obviated by adding brine or water in quantities of about 1 to about 5 volumes water per volume of emulsion to the emulsion, preferably a water-in-oil emulsion. The mixture is allowed to separate by gravity into two phases, an oily emulsion phase and an aqueous phase. Thereafter, the oily phase is employed as the produced emulsion in the extraction treatment.

The concentration of the extraction compounds added varies considerably with the different compounds employed. The cumene sulfonate salts and propylbenzene sulfonate salts may be effective at concentration levels ranging from about 0.3% to about 6.0% by volume, preferably about 0.8% to about 2.0% of the brine employed. The ethyl benzene salts generally require concentration levels about 50% higher than the cumene and propyl benzene sulfonate salts, while the dicyclopentadiene sulfonate salts require about twice the concentration and the xylene sulfonate salts about two and a half times the concentration of the cumene sulfonate salts.

The alkanols as second extracting compounds should be added to the middle phase in amounts of about 0.5% to about 3% volume of alkanol per volume of middle phase. Isopropanol and n-propanol are preferably added in volumes of about 0.75% to about 2.0% of the first midphase volume. The other alkanols usually require slightly greater quantities to perform effectively.

The lowest effective concentration of extraction compound required also varies substantially with the concentration of surfactants in the produced emulsion, the treating temperature, the salinity of the brine, and the types and concentrations of solubilizers and surfactants in the produced emulsion. For example, a larger amount of extracting compound is required as surfactant concentration in the produced emulsion increases and as the extraction temperature increases. Higher brine salinities also require higher extracting compound concentrations.

The surfactant extraction is most effectively carried out at a temperature of about 35° C. to about 70° C., with about 45° C. to about 60° C. being the most preferred temperature range. Ideally, the produced emulsion and the extracting compound and/or extracting compound solution is preheated to the extraction temperature prior to mixing. But it should be noted that extractions can be successful with certain produced emulsions even at ambient temperatures. The temperature of extraction should be increased when excessive surfactant remains in the aqueous phase after treatment. Conversely, extraction temperature should be decreased when excessive surfactant remains in the water-free and normally surfactant-free oil phase.

Several other corrective steps are available to solve the problem of excessive surfactant remaining in the normally brine-free and surfactant-free oil phase and oil-free aqueous phase. Excessive surfactant in the aqueous phase may be remedied by the addition of brine or water in the initial treating step to reduce the extracting compound concentration. The addition of divalent ions such as calcium and magnesium will also reduce surfactant remaining in the aqueous phase. Increasing the extracting compound concentration will usually remedy the problem of excessive surfactant remaining in the normally surfactant-free and brine-free oil phase.

The preferred embodiment of the extraction method also includes the concurrent addition with the first extracting compound of about 0.1% to about 3% by volume, preferably about 0.5 to about 1.5% of a water soluble sulfonate having an equivalent weight of about 250 to about 450. This results in a substantially decreased middle phase volume having an increased concentration of surfactant contained therein. As before, the oil phase remains substantially surfactant-free and brine-free and the aqueous phase remains oil-free. An especially preferred water-soluble sulfonate is the compound sold under the tradename TRS-40 by Witco Chemical Company having an equivalent weight of about 350.

If the produced emulsion was an oil-in-water emulsion to which a substantial amount of an oil soluble sulfonate such as TRS-18 was added to reduce its volume and change the emulsion to a water-in-oil emulsion, then it may be necessary to add over 1.5% of the water soluble sulfonate.

The extraction method may be practiced in either a batch or continuous manner. Most of the extracting compound is partitioned into the oil-free aqueous phase. Thus, the aqueous phase may be recycled and used to treat additional produced emulsion. But since some extracting compound is lost to each middle phase, additional extracting compound must be added to the used aqueous phase before they are employed again for additional extraction.

For continuous surfactant extraction, it is suggested that a pair of apparatus similar to the widely used, vertical type heater treater or similar to the apparatus disclosed in U.S. Pat. Nos. 2,354,856 and 2,753,046 be employed. The suggested apparatus consists of a vertical cylindrical vessel having perforated plates or baffles spaced throughout the vessel to minimize turbulence in the treating vessel. One vessel is employed for the first extraction step and a second vessel is used for the second extraction. If it is desired to use the single step embodiment of the invention, one vessel should be used for both extracting compounds.

Each vessel should contain a column of brine having dissolved therein the respective extracting compound with the column maintained at a constant extraction temperature between about 35° C. and about 70° C. The produced emulsion is treated by injecting it at the bottom of the vessel and dispersing it within the extracting compound solution by conventional techniques such as impellers, atomizing jets, or static mixers without causing significant turbulence in the upper part of the liquid column. In rising through the column of brine and extracting compound, surfactants are extracted from the dispersed crude oil droplets. At the top of the column, substantially surfactant-free and brine-free crude oil is withdrawn while the surfactants, in the form of a middle phase emulsion, collect in the zone between the water-free crude oil and the aqueous phase. The first middle phase is withdrawn whenever a predetermined volume is exceeded and then transferred to the second vessel for the second extraction. The solution of brine and extracting compound remains in the vessel and is supplemented with additional extracting compound and brine when needed.

Automatic maintenance of the volumetric ratio of the phases is accomplished by placing sensors within at least two of the phases. The first sensor is set at the bottom of the crude oil phase to detect any significant increase in surfactant or brine concentration of the crude oil, with any such increase triggering the introduction of concentrated extracting compound solution into the fluids entering the vessel. A second sensor is set to detect any significant increase in surfactant or oil in the bottom aqueous phase, with any such increase triggering the introduction of dilute extracting compound solution or brine into the fluids entering the vessel. In a like manner, the sensors terminate the flow of additives when phase volumes and composition normalize. Conductivity-resistivity sensors and FT-IR (Fourier Transform-Infrared Spectroscopy) sensors are examples of instrumentation suitable for electronic transmission of start-stop signals to the pumps controlling introduction of extracting compound solution.

Gas evolution from the emulsions to be treated can be minimized by pressurizing the treating vessel or by pretreating the emulsions to remove such gases. It is further suggested that a portion of the treated, surfactant-free oil be recirculated to act as a diluent for the produced emulsion entering the vessel. Under certain conditions, this will increase extraction efficiency.

The relatively low volume middle phase from the second extraction containing a high concentration of surfactants may be directly injected into the formation as a surfactant slug in a chemical flood, thus, reutilizing the originally injected surfactant. The use of the middle phase of the present extraction invention as a surfactant slug in chemical flooding can produce a substantial savings in the quantities of relatively expensive surfactants that are employed for such flooding, significantly improving the economics of surfactant flooding.

The middle phase may be injected "as is" or in conjunction with other materials as a substitute for the surfactant flooding slug. Recovery efficiencies with the "as is" middle phases will often substantially approach the recovery efficiencies of the originally injected surfactant floods. When the second middle phase is supplemented with additional solubilizers, surfactants, or most preferably, the originally injected surfactant flooding composition, total recovery efficiencies usually equal or surpass the recovery efficiencies of the original flooding composition. Depending on the composition of the emulsions and the formation to be flooded, it is preferred that the second middle phase be mixed with the surfactant composition originally injected in ratios of about 3:1 to about 1:3.

It has also been discovered that the addition of various solubilizers to the middle phase in concentrations ranging from about 0.3% to about 3% increases recovery efficiency under certain conditions. A preferred solubilizer is a composition of sulfated derivatives of alkoxylated alcohols sold under the tradename Alfonic 1412A by Conoco Inc. added in the preferred concentration range of about 0.5% to about 1.5%.

The addition of Alfonic 1412A to a polymer slug following the surfactant also solves two problems encountered in the reutilization of the middle phase in a surfactant slug for chemical flooding. It has been noted in some instances that the injection of a polymer slug following the middle phase significantly increases the pressure change as well as increasing surfactant loss to the core matrix. However, the addition of the Alfonic 1412A solubilizer to the polymer slug in ranges of 0.5% to 1.0% produces a pressure differential and surfactant loss similar to the originally designed surfactant slug and also improves recovery efficiency to a value substantially equal to or surpassing that of the originally designed surfactant system.

The following examples further illustrate the novel surfactant extraction and reutilization method of the present invention. These examples are given by way of illustration and not as limitations on the scope of the invention. Thus, it should be understood that the steps and materials employed in the instant method may be varied to achieve similar results within the scope of the invention.

EXAMPLE 1

A water-in-oil emulsion was prepared to simulate the produced emulsions from a West Texas field in the Permian Basin. The following ingredients were mixed at an elevated temperature of about 40 to 54° C.: 100 cm³ of the surfactant slug employed in the Permian Basin field, 100 cm³ of crude oil from the field and 250 cm³ of formation brine. The 100 cm³ of surfactant slug had the same make up of that used in the Permian Basin field, containing 1.6% Witco TRS-18, 1.86% Witco TRS-40, 1.55% Alfonic 1412A, 0.95% sodium cumene sulfonate, 4% gas oil, 4% clean crude oil from the same field, 10% fresh water and formation brine for the remainder.

The prepared emulsion soon separated into two phases, an upper, surfactant-containing water-in-oil emulsion and a lower aqueous phase. 200 cm³ of the Permian crude was added to the upper emulsion phase. 350 cm³ of the above diluted water-in-oil emulsion was extracted with 350 cm³ of formation brine containing 1.8% sodium cumene sulfonate (SCS) at 54° C. Volumes of the three phases are listed below.

Upper Oil Phase--265 cm³

Middle Phase--69 cm³

Lower Aqueous Phase--352 cm³

The second extraction step was performed on the middle phase with a quantity of isopropanol (IPA) equal to 2% of the volume of middle phase. This extraction was effective in inducing a further three phase separation of the first middle phase at 54° C. 50 cm³ of the first middle phase split into:

Upper Oil Phase--7.5 cm³

Middle Phase--34.0 cm³

Lower Aqueous Phase--8.2 cm³

The second extraction treatment with isopropanol released a significant portion of the crude oil from the first middle phase formed during sodium cumene sulfonate extraction. A new aqueous phase also formed which later tests indicated could be recycled for use in further extractions. 1 cm³ of isopropanol released an additional 7.5 cm³ of oil from the first microemulsion middle phase.

FT-IR analyses were run on the various phases, giving the below results in Table I.

                  TABLE I                                                          ______________________________________                                         Sample          Surfactant, %                                                                              Oil, %  Brine, %                                   ______________________________________                                         1.  Dilute w/o emulsion                                                                            1           88    11                                       2.  SCS extrn. phases                                                              a. lower aqueous                                                                               1(SCS)      0     99                                           b. middle       6           31    63                                           c. upper oil    0           100   0                                        3.  IPA treated midphase                                                           a. lower aqueous                                                                               ˜2.5  trace 97.5                                         b. middle       10.5        28.5  61                                           c. upper oil    0           100   0                                        ______________________________________                                    

The FT-IR analyses indicated that the EOR surfactants (TRS-18, TRS-40, Alfonic 1412A) remain concentrated in the mid-phase after the second extraction by 2% by volume isopropanol. Thus, the resulting middle phase from the second extraction can be recycled for injection with much the same results as the first extraction middle phase reinjection for chemical flooding in Examples 23-26.

EXAMPLES 2-4

The procedure of Example 1 was followed again, but 1% by volume isopropanol was added in the second extraction step instead of the 2% by volume quantity used in Example 1. 32 cm³ of the first middle phase microemulsion was extracted with 0.32 cm³ of isopropanol at 54° C. This extraction yielded three phases of

Upper Oil Phase--2.8 cm³

Middle Phase--24.2 cm³

Lower Aqueous Phase--3.4 cm³

Although proportionately less clean oil was removed from the first middle phase when the second extraction was performed with 1% isopropanol instead of 2% isopropanol, the oil/isopropanol ratio increased to 9/1 from 7.5/1. Thus, under some conditions, economics may dictate 1% isopropanol as the quantity of choice.

In Examples 3 and 4, other extraction runs were performed with 3% and 4% isopropanol. The 2% isopropanol addition gave the optimum extraction of salable oil.

EXAMPLES 5-6

The procedure of Example 1 was again repeated, but with 1% and 2% by volume of 1-propanol per volume of first middle phase. These extractions yielded approximately the same volume of free oil upper phase as did the isopropanol extractions at 54° C. and slightly larger volume aqueous phases.

EXAMPLES 7-8

2% isopropanol/ethanol blends in 1/1 and 3/1 ratios were used for Examples 7 and 8, respectively, following the Example 1 procedure. Although the 1/1 and 3/1 blends of isopropanol to ethanol gave smaller free oil phases than did 2% isopropanol alone, an ethanol blend may be cost effective because of the substantially lower price of ethanol. Both blends caused additional oil and brine to partition from the middle phase increasing the volumes of the upper oil phases and lower aqueous phases.

EXAMPLES 9-11

2% by volume quantities of methanol, ethanol and isobutanol were employed in Examples 9-11, respectively, following the general procedure of Example 1. But in these three examples the middle and lower phases from the first extraction were mixed together and all second extracting compound solutions were added before the mixture separated.

The shorter chain alcohols, methanol and ethanol, gave less free oil separating out than did the isopropanol of Example 2. The isobutanol extraction of Example 11 tended to leave surfactant in the oil, an undesirable result.

EXAMPLES 12-14

Three runs were performed with 1/1, 3/1 ratios of isopropanol/isobutanol and with 100% isopropanol in 1% quantities by volume in Examples 12-14, respectively, following the procedure of Example 1. 5 cm³ first middle phase portions were mixed with 0.05 cm³ of alcohol and aged at 54° C.

The same volume of free oil separated out with the isopropanol/isobutanol blends as with the isopropanol extractions. Brine volume in the lower aqueous phase did increase, however, with the isopropanol/isobutanol blends.

EXAMPLES 15-22

Multiple extraction tests for the first extracting compound were run on the emulsion employed in Example 1. One volume of water-in-oil emulsion was diluted with two volumes of surfactant-free crude oil from the West Texas field. The emulsion and oil blend containing 1% surfactant and 4.5% brine (according to FT-IR analysis) was extracted at 55° C. with an equal volume of brine from the West Texas field to which the test extracting compounds were added. Table III lists the minimum concentration of the first extracting compound required to yield three phases, including a substantially surfactant-free and water-free oil phase, a middle-phase and a oil-free aqueous phase.

                  TABLE II                                                         ______________________________________                                         EX-                                                                            AM-                           REQUIRED                                         PLE  EXTRACTING COMPOUND      CONC, %                                          ______________________________________                                         15.  Benzene sulfonate, sodium salt                                                                          6+                                               16.  Toluene sulfonate, sodium salt                                                                          6+                                               17.  Xylene sulfonate, sodium salt                                                                           3.9                                              18.  Ethyl benzene sulfonate, sodium salt                                                                    2.5                                              19.  Cumene sulfonate, sodium salt                                                                           1.7                                              20.  Naphthalene sulfonic acid*                                                                               0.85                                            21.  Dicyclopentadiene sulfonate, sodium salt                                                                3.1                                              22.  Alfonic 1412A            No Phase                                                                       Separation                                       ______________________________________                                          *Na.sup.+  salt not soluble in brine                                     

The results indicated that the most effective type of first extracting compound was a benzene ring with a two to three carbon chain attached. The cumene, xylene, and ethyl benzene sulfonates were the most effective extraction compounds tested. The sodium dicyclopentadiene sulfonate was also effective at about twice the required concentration for sodium cumene sulfonate. Aromatic rings with substantially longer alkyl side chains are much less water soluble and consequently, are not effective extracting compounds for this process.

The naphthalene sulfonic acid could not be tested as a sodium salt, but was effective at relatively low concentrations in the acid form. However, naphthalene sulfonic acid is a highly corrosive chemical.

A solubilizer, Conoco's Alfonic 1412A was also tried as an extracting compound. Low, medium and high concentrations of 1412A failed to produce phase separation into the three distinct phases of the present invention.

EXAMPLES 23-26

Comparative core floods were performed with the middle phases from the first extraction only of the emulsion of Example 1. These floods were conducted at 43° C. in a Baker Limestone core having a length of 30.5 cm, a pore volume of 130 cm³ and a permeability of 58 millidarcies. The connate fluids in the core were brine from the Permian Basin field and clean crude from the same field containing 25% added heptane. Chemical slug size was 0.18 pore volume in all floods, followed by continuous injection of a 1,000 ppm polysaccharide polymer in deionized water, sold under the trademark Rhodopol by Rhone-Poulenc Chemical Co.

Four floods were undertaken. The first was a core flood with the surfactant slug originally injected at the Permian Basin field. The second core flood employed the first middle phase from the first extraction of Example 1 with 0.1% TRS-18 added. The third core flood consisted of the first middle phase plus 0.1% TRS-18 and 0.1% Alfonic 1412A. The fourth core flood was comprised of two thirds of the originally injected surfactant slug plus one third first middle phase from the first extraction process of Example 1 and 0.033% TRS-18. The results are listed below.

                  TABLE III                                                        ______________________________________                                         NET RECOVERY EFFICIENCY (%) OBTAINED                                           BY FLOODING                                                                                     Pore Volumes                                                                   0.5 0.75    1.0   1.25  1.5                                   ______________________________________                                         23. Original Surfactant Slug                                                                           8    30    45  57    61                                24. Midphase + 0.1% TRS-18                                                                            14    33    45  52    58                                25. Example 24 + 0.1% 1412A                                                                           14    36    45  47    47                                26. 2/3 Example 23 + 1/3                                                                               6    22    42  52    59                                    Example 24                                                                 ______________________________________                                    

The table shows that the recovery efficiencies for all of the floods containing the first middle phase were slightly lower than the originally designed system per pore volume injected. However, the amount of surfactant in the middle phase floods was probably lower than that of the originally designed surfactant system.

Best results with the middle phase were obtained with the fourth core flood consisting of one third middle phase, two thirds originally injected surfactant slug and 0.033% TRS-18. This blend of original surfactant slug and middle phase at a two to one ratio achieved a relatively high recovery efficiency of 61%, the same as that of the original designed surfactant slug, but at a greater injected pore volume of about 1.6 compared to about 1.35. The fourth core flood suggests that blending of the originally injected surfactant with the middle phase from the extraction process is an effective technique for reutilizing surfactants.

Many other variations and modifications may be made in the concepts described above by those skilled in the art without departing from the concepts of the present invention. Accordingly, it should be clearly understood that the concepts disclosed in the description are illustrative only and are not intended as limitations on the scope of the invention. 

What is claimed is:
 1. A method for extracting and concentrating enhanced oil recovery surfactants into a relatively small volume surfactant-rich middle phase from produced emulsions comprising oil, water and surfactant, which comprises:mixing a produced emulsion with an extracting compound solution of water containing about 0.3% to about 6.0% of a first extracting compound selected from the group consisting of the alkali metal salts and ammonium salts of propyl benzene sulfonate, cumene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate; allowing the mixture of produced emulsion and first extracting compound solution to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a first relatively low volume middle phase containing surfactant, oil and water, and an oil-free aqueous phase; mixing a second extracting compound with said first relatively low volume middle phase in the quantity of about 0.5% to about 3% volume per volume of first middle phase, said second extracting compound consisting of an alkanol having two to four carbon atoms; and allowing the mixture of first low volume middle phase and alkanol to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a second relatively smaller volume surfactant-rich middle phase containing surfactant, oil and water, and an oil-free aqueous phase.
 2. The method of claim 1, wherein the produced emulsion is processed through a heater treater to reduce the volume of emulsion to be mixed with the first extracting compound solution.
 3. The method of claim 1, wherein the water containing the first extracting compound is a brine.
 4. The method of claim 1, wherein the alkanol is added to the first middle phase in an aqueous solution.
 5. The method of claim 1, wherein all of the steps of mixing and allowing the mixtures to separate are carried out at a temperature of about 35° C. to about 70° C.
 6. The method of claim 5, wherein the extraction with alkanol is carried out at an increased temperature when excessive surfactant remains in the aqueous phase from extraction of the middle phase.
 7. The method of claim 5, wherein the extraction with alkanol is carried out at a decreased temperature when excessive surfactant remains in the oil phase from extraction of the middle phase.
 8. The method of claim 1, wherein either oil-free aqueous phase is supplemented with additional extracting compound and mixed with an emulsion phase for subsequent extractions.
 9. The method of claim 1, wherein divalent ions are added to said first middle phase when excessive surfactant remains in the aqueous phase after extraction with alkanol.
 10. The method of claim 1, wherein the amount of the alkanol mixed and added to the first middle phase is increased when excessive surfactant remains in the oil phase.
 11. The method of claim 1, wherein the alkanol is ethanol.
 12. The method of claim 1, wherein the alkanol is n-propanol.
 13. The method of claim 1, wherein the alkanol is isopropanol.
 14. The method of claim 1, wherein the alkanol is butanol.
 15. The method of claim 1, wherein the alkanol is isobutanol.
 16. The method of claim 1, wherein a mixture of isopropanol and ethanol is employed.
 17. A method for extracting and concentrating enhanced oil recovery surfactants into a relatively small volume, surfactant-rich middle phase from produced emulsions comprising oil, brine and surfactant, which comprises:allowing the produced emulsion to settle into two phases, an emulsion phase and an aqueous phase; mixing the emulsion phase with a brine solution containing about 0.1% to about 3.0% of a water soluble sulfonate surfactant and about 0.3% to about 6% of a first extracting compound selected from the group consisting of the sodium salts of propyl benzene sulfonate, cumene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate at a temperature of about 40° C. to about 65° C.; allowing the mixture of emulsion, and first extracting compound and water soluble sulfonate solution to separate at a temperature of about 40° C. to about 65° C. into at least three phases, including a substantially surfactant-free and brine-free crude oil phase, a first relatively low volume middle phase containing surfactant, oil and brine and an oil-free aqueous phase; mixing isopropanol in the quantity of about 0.5% to about 3.0% volume per volume of first middle phase with said first middle phase at a temperature of about 40° C. to about 60° C.; and allowing the mixture of first middle phase and isopropanol to separate at a temperature of about 40° C. to about 65° C. into at least three phases, including a substantially surfactant-free and brine-free crude oil phase, a second relatively small volume, surfactant-rich middle phase containing surfactant, oil and brine, and an oil-free aqueous phase.
 18. A method for extracting and concentrating enhanced oil recovery surfactants into a relatively small volume surfactant-rich middle phase from produced emulsions comprising oil, water and surfactant, which comprises:mixing a produced emulsion with an extracting compound solution of water containing about 0.3% to about 6.0% of a first extracting compound selected from the group consisting of the alkali metal salts and ammonium salts of propyl benzene sulfonate, cumene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate; allowing the mixture of produced emulsion and first extracting compound solution to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a first relatively low volume middle phase containing surfactant, oil and water, and an oil-free aqueous phase; mixing the first middle phase and aqueous phase together and allowing them to separate into upper and lower phases; mixing a second extracting compound in the quantity of about 0.5% to about 3.0% volume per volume of said upper phase with said upper phase, said second extracting compound consisting of an alkanol having two to four carbon atoms; and allowing the mixture of said upper phase and alkanol to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a second relatively small volume, surfactant-rich middle phase containing surfactant, oil and water, and an oil-free aqueous phase.
 19. A method for extracting and concentrating enhanced oil recovery surfactants into a relatively small volume surfactant-rich middle phase from produced emulsions comprising oil, water and surfactant, which comprises:mixing a produced emulsion with an extracting compound solution of water containing about 0.3% to about 6.0% of a first extracting compound selected from the group consisting of the alkali metal salts and ammonium salts of propyl benzene sulfonate, cumene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate; allowing the mixture of produced emulsion and first extracting compound solution to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a first relatively low volume middle phase containing surfactant, oil and water, and an oil-free aqueous phase; mixing the first middle phase, aqueous phase and an alkanol having two to four carbon atoms together, said alkanol mixed in the quantity of about 0.5% to about 3% alkanol volume per combined volume of middle and aqueous phases; and allowing the mixture of said first middle phase, said aqueous phase and said alkanol to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a second relatively small volume, surfactant-rich middle phase containing surfactant, oil and water, and an oil-free aqueous phase.
 20. A method for reutilizing surfactants in a surfactant flood that are entrained within a produced emulsion comprising oil, water and surfactant, which comprises:allowing the produced emulsion to settle into two phases, an emulsion phase and an aqueous phase; mixing the emulsion phase with an extracting compound solution of water containing about 0.3% to about 6.0% of a first extracting compound selected from the group consisting of the alkali metal salts and ammonium salts of propyl benzene sulfonate, cumene sulfonate, ethyl benzene sulfonate, methyl ethyl benzene sulfonate, diethyl benzene sulfonate, methyl propyl benzene sulfonate, xylene sulfonate and dicyclopentadiene sulfonate; allowing the mixture of emulsion and first extracting compound solution to separate into at least three phases, mixing a second extracting compound with said first middle phase in the quantity of about 0.5% to about 3% volume per volume of first middle phase, said second extracting compound consisting of an alkanol having two to four carbon atoms; allowing the mixture of first middle phase and alkanol to separate into at least three phases, including a substantially surfactant-free and water-free crude oil phase, a second relatively lower volume, surfactant-rich middle phase containing surfactant, oil and water, and an oil-free aqueous phase; and injecting the second middle phase as a surfactant slug in a surfactant flood.
 21. The method of claim 20, wherein the second middle phase is mixed with a surfactant and injected as a surfactant slug in a surfactant flood.
 22. The method of claim 20, wherein about 0.3% to about 3.0% of a solubilizer is added to the middle phase prior to injection as a surfactant slug in a surfactant flood.
 23. The method of claim 22, wherein the solubilizer is comprised of sulfated derivatives of alkoxylated alcohols.
 24. The method of claim 20, wherein the middle phase is mixed with a composition and then injected as a surfactant slug in a surfactant flood, said composition being the same in makeup as the surfactant slug originally injected into the formation.
 25. The method of claim 20, wherein a polymer slug is injected into the formation after the injection of the middle phase, said polymer slug containing a solubilizer. 